This invention relates to a biodegradable plastic material and a method of preparing same.
There is an increasing demand for a plastic material which is decomposed by the action of microorganisms, (bacteria, yeast, fungi, etc.) or enzymes, thereby destroying to the original shape.
One well known biodegradable plastic material includes a mixture of starch with a synthetic polymer such as a polyethylene (ANTEC' 89, 1351-1355), an ethylene/acrylic acid copolymer (US-A-4,138,784 and 4,337,181) or an ethylene/vinyl alcohol copolymer (JP-A-Hei-3-31333).
In the above polyethylene-containing plastic material, the starch is present as a filler within a matrix of the polyethylene which is not biodegradable. Thus, the biodegradability of this material is not satisfactory. While the plastic material containing the ethylene/acrylic acid copolymer has superior water resistance and mechanical properties as compared with the polyethylene-containing plastic material, the biodegradability is less satisfactory. Regarding the ethylene/vinyl alcohol copolymer-containing plastic material, the composition of the copolymer is not disclosed so that it is not clear whether or not the copolymer is biodegradable. This material has a problem in that pin holes are apt to be formed in films obtained therefrom because bubbles are unavoidably formed by vaporization of water during kneading of the raw materials.